Archive for the 'Proportional Symbol' Category

Today’s effort comes to my attention via a reader, Nicholas, who wrote to me early last year and suggested that I have a look at the following piece:

Click to enlarge

It was created by Chris Dickersin-Prokopp, who posted it on his blog and on Greater Greater Washington (where it got most of its comments) in February 2013. If you read the comments, you can see that, unfortunately, the response was not quite as positive he had hoped for. Not only did Mr. Dickersin-Prokopp accept the criticism gracefully, but he said he hoped that perhaps he’d find his way onto the pages of this very blog. So, let’s have a look.

To me, the real issue here is not in the map design itself, but instead the disconnect between the author and his readers. It’s an issue in any sort of creative field: you make something, and it turns out that the people who view that something were looking for something else. Mr. Dickersin-Prokopp’s detractors seemed to be looking for details on the map:

“Wow. I find it hard to think of a worse way to visualize these data. How am I supposed to draw any conclusions from a picture showing thousands of overlapping circles?”

“I can’t tell how many overlapping circle I’m looking at in different areas. Why not just make each sale a dot and color code the dots for different sales price ranges?”

But the author, I speculate, was trying to paint a broad picture: where, generally, home sales are more concentrated and more expensive. Counting individual circles isn’t necessary here. You just need to be able to tell where there are roughly more or roughly less. I think that his map does this job just fine, giving you the 10-second quick understanding of the basic pattern. His readers, however, were looking for something else: a map that let them break these patterns down in more detail, and count the number of houses in neighborhoods (everyone always wants to know what’s going on in their neighborhood/city/state when they see a map). The map isn’t ready to do that, as is, and the second quote above suggests a reasonable alternative. But one that, probably, wouldn’t have done as good a job at telling the quick broad story.

Two different ways of reading the same set of data: the big pattern, and the individual location data. The author had one in mind, but some of his commenters had another. What to do? Well, there may well have been a good symbology to satisfy both. But, setting that aside, how do we get people on the same page as us if we’re making maps? I think this map could use a little more context, to steer people’s minds toward reading it as the author wishes. Annotations would be handy—highlight some region or other and say, “over here, we can see a dense area of inexpensive home purchases that happened because of Reason X.” Get people thinking about the patterns and pull them away from the details that the author is less focused on.

The other option is to just change the map in response to comments, trying to give the audience what they’re looking for. It’s tough, as a creator, to have to give up on part of your vision and preferences, but it’s necessary if you want anyone to look at your creation. If no one likes it, then it doesn’t matter how great you think it is: no one is looking. Of course the hard part about that is that while many don’t agree with your choices, they don’t agree with each other, either. Some folks liked Mr. Dickersin-Prokopp’s effort:

“The message the map intends to convey is clear and obvious.”

If he changes things, he may displease some folks who were previously happy. There’s not much to be done about that, except to accept that you can’t please everyone.

Bigger picture aside, there are some other interesting things to dissect here, starting with the legend. which states, “Circle size represents sale price. One square meter equals one dollar.” If I interpret this correctly, this means that, in order to divine the sale price of a home you must determine how large a circle when compared against the map scale. That is, you pretend the circle is a real area of land in DC, measure the size of that land, and then convert to dollars. This is quite a fascinatingly weird way of explaining the symbology, and I’ve never seen anything like it. For good reason: it’s difficult enough so as to be largely useless. If you want people to understand what symbols mean, show the symbols; a legend should show more than it should tell. It would be better if this particular map showed people some sample circles and the values they represent. Then readers can reasonably eyeball things.

Typical proportional symbol legend designs. Via Esri Mapping Center.

It’s highly unlikely that anyone is planning on measuring the exact price of each home (and if they do, they deserve what they get). We just need to let them get a rough idea of the pattern, and the circles above do that easily, without requiring people to visually measure square meters.

Speaking of which, that brings us to the scale. The increments could be a lot more helpful. At the very least, they should be in kilometers, but miles would be likely much more intelligible to an US audience. And the scale bar probably doesn’t need to be as wide as DC itself. No one is likely to do any measurements with it. To that end, I’d argue it could be dropped altogether. It is an unnecessary map element.

One Nice Thing: Putting your work out there for criticism and comment is tough, especially if you’re opening it up to the harsh gaze of the random Internet visitor. Mr. Dickersin-Prokopp handled the experience gracefully, and listened to the feedback he received, where I’ve seen other people in similar situations try to rationalize away criticism, or strike back angrily. Kudos to him.

This morning, a friend emailed me a link to this story at the Daily Mail, which contains a number of beautiful maps on America’s infrastructure networks. Go check it out; I’ll wait here while you spend fifteen minutes going “ooh!” and “ahh!” at all the images.

While they are beautiful, they are not without problems. Lovely visuals, deep conceptual errors. Let’s start with the one that stuck out to me, the visualization of job losses. At least, I assume it’s job losses. The caption at the Daily Mail reads, “Unemployment: The number of job losses in the U.S. chronicled in this stunning image.” Unemployment is different than job losses, so I’m not sure which is being mapped, but I suspect the latter.(EDIT: I’ve lately found the video that these maps come from. This is actually a map showing the distribution of manufacturing jobs in the 1990s. In the video, the dots wink out — turn black — to show the decline of the manufacturing sector. Seen at about 12 min, 50 sec in the video here: http://www.pbs.org/america-revealed/episode/4/)

A dot density map is approximately the worst way to look at a data set like this. The author(s) took the number of jobs lost in each state, converted that to a certain number of dots, and then scattered those dots all throughout the state. The result is misleading in several ways. First off, this is really a map of job loss density. The brightest areas are where the dots are clustered, which means a lot of jobs were lost in a tight space. Texas lost a lot of jobs, probably as many as Ohio or Illinois (I’m not going to count every dot, but they probably have similar numbers). But the latter two states look worse off, because they have about the same number of dots crammed into a smaller physical area. Actually, it’s not even a map of job loss density, because the areas of the states are distorted due to curvature of the Earth in this view. Washington, for example, is a lot smaller than if we were looking at it from directly above, and its unemployment picture therefore looks worse. So, this isn’t really a map of “job losses” so much as it’s a map of “job losses divided by the size of each state, if you distort the sizes of the states a lot.”

So, reading the dot concentrations will simply mislead us. But what about the number of dots? If we painstakingly counted them, we could certainly find out at least how many jobs were lost in a state without having to worry about this density issue. Well, the second big problem is that these data aren’t normalized to population. There are a lot more dots in Illinois than in Wyoming. This is because Illinois is a very populous state, whereas no one lives in Wyoming. No account was taken, seemingly, of population differences. Some states are being hit harder by the recession than others, but all you can tell from this map is that places that had more people lost more jobs. I quickly found this table prepared last year and it points out that Nevada has been hammered by the downturn, losing 8% of its jobs. Ohio, on the other hand, lost only 2.6%. But when you look at the map, which state looks worse off?

Lastly, jobs weren’t lost evenly throughout each state, so why scatter the dots evenly? Probably because the author(s) only had state-based data, but making some account for population locations would be nice. Why show a sea of lost jobs in eastern California, which is mostly desert, mountains, and unpopulated forests? The exact locations of the dots are meaningless anyway, since they’ve been distributed randomly in each state.

This map should have been a choropleth of job losses per state divided by population. It’s not nearly as sexy, but it’s also not seriously misleading.

(EDIT: As said, this critique was based on an inaccurate description of what this map is about, and I apologize for not doing my research. Much of the critique still stands — showing dots still seems odd for this data set. It’s a map of “manufacturing jobs divided by the size of each state, if you distort the sizes of the states.” The need for normalization is probably less, as well, though it couldn’t hurt.)

The dot density map was what galled me. On the other hand, my friend Chris, who sent me the link, was bothered by the map of wireless access towers:

I can’t say for certain without hearing the accompanying narration (EDIT — see below), but the author(s) very likely received a data set which had point locations for towers and broadcast power, and simply made circles proportional to the power. That’s all quite reasonable, but the map very much looks like it’s trying to portray the actual signal coverage areas, and that’s a very different thing. Most any electromagnetic signal coming from a tower is not going to move in a perfect, even circle away from the transmission point. It gets distorted by a lot of things — buildings get in the way, so do mountains and other terrain features, and the Earth’s magnetic field also affects it. And if it’s been broadcast by a directional antenna, the signal starts out stronger in some directions than others. Presenting these transmissions as circles is an overly idealized view of how they work. Even if the authors were only using circles as a symbol for power, rather than suggesting these are areas of coverage, a lot of people are going to misunderstand this as the latter. Every reader brings their own interpretations to the map, and it’s not always the one the author wants. The best you can do is try and head them off.

(EDIT: Again, I’ve now looked up the relevant section in the video to figure out what they map is actually of. It’s found at 40:20 in this video: http://www.pbs.org/america-revealed/episode/4/ — the narrator doesn’t actually say what the map is of; it just shows while he talks about how your wireless signal is bounced between towers, so I’d say the critique above stands as is. If anything, I’d say my point about misunderstanding the map is even stronger, because the program really does leave it up to you to figure out what’s going on.).

All the maps on this site have a pseudo-realistic appearance, and they’re even discussed as though you’re “seeing what the nation looks like from the skies.” My colleague Marty Elmer pointed out to me that this realism means an increased expectation of accuracy. If you’re telling me that I’m floating above the US, really seeing the job losses or broadcast signals, I’m likely to believe that this is really how things are distributed on the ground. That the signals really are circles, or the jobs really were lost in the woods of northern Michigan. I’m less likely to take the thematic data as an abstraction because the base map, with its fancy lighting effects and clouds, doesn’t look very abstracted. Generalization is not just about redrawing your linework to the right scale; it’s about credulity. This was one of the biggest points I would emphasize to my students back when I lectured on the subject. Visual abstraction needs to match data abstraction. Readers seeing a highly simplified visualization will assume the data are likewise telling a highly simplified story. If they see a very realistic and detailed basemap, they’re likely to assume that the data have been treated similarly.

In the end, we’re left with beautiful, but potentially (or sometimes outright) misleading images, and that’s a travesty. These are for a television special, and besides going in front of millions of eyes on PBS, these works will very likely go around the Internet to millions more. The maps are lovely to look at, and this means they’ll get a chance to misinform many, many more people. It’s a shame, because it’s a squandered opportunity to inform people about actual facts. Imagine pairing quality visuals with well-thought-out data treatment and map concepts, and how far that would go. But infotainment isn’t about the substance, just the style. See the headline to that Daily Mail link, for example — “Secret corpse flights,” as though this transport of bodies were illicit, rather than a routine movement of your loved ones to their desired resting place. It makes a good story, even if it’s not true.

One Nice Thing: I could go on for a long time about how excellent these look. Maps need to be beautiful if you want people to look at them and spend the time to learn something off them. I’d love to see the author(s) continue to do this great work, just with better data and ideas for portraying it.

Good day, gentle readers. I am lately returned from a couple of trips to lands outside of Wisconsin. NACIS was wonderful, and it was great to meet many of you in Sacramento. While there, I learned that Tom Patterson, creator of the Kenai Fjords map which I praised in my last post, was slightly disappointed that I did not point out anything negative about his work. Looking it over again, I will say that, for the elevation marker points on his map (mountain tops and sea valleys), the labels positioning could be more consistent.

I’m really nitpicky. My students love it. At least, that’s how I interpret their annoyed stares.

The subject of today’s post is once again one of my own works. This is in response to a conversation with my adviser, Mark Harrower, who pointed out that most any map, from the best to the worst, could be improved by some critique. I have previously featured one of my worst maps on here — Mark challenged me to instead show him one of my best, and then post his comments on it. So I picked my favorite, a map about the tallest buildings in Europe during the last 125+ years:

Rising Skyline, by Daniel Huffman

Rising Skyline detail

Legend

Here’s what Mark had to say (and he warns that some of these are nitpicky — his students, too, love it):

He’s quite right – I’m always embarrassed by this sort of thing, forgetting to design for people with abnormal color vision. Actually, I’m surprised that it was Hospital (pink) and Museum (grey) that got him. I would have figured on Religious (red) and Residential (green), but I suppose those two colors are distinct enough in lightness that they’re still separable.

“I don’t like that you have both vertical and horizontal timelines, it requires too much work to get this, and the vertical timeline took some time for me to understand in part because going down is more recent. Physical geographers/geologists like their vertical timelines too, but I think they arrange them with newest at top? Nonetheless, for most users I suspect a left-to-right timeline would be more graspable (oldest on left).”

When I started putting this map together, one of the people I showed it to didn’t like the “empty” spaces along the left and bottom of the map. I responded by adding in these timelines. This is probably one of the worst justifications you can give for adding something to a map: “I needed to fill space.” The vertical timeline was vertical because I needed to cover a vertical space. I think the data are interesting, to be sure, and related to the subject of the map, but it could do without such a timeline. Or a much smaller one. I did a redesign of this map recently for inclusion in a textbook. I had to shrink it from its normal size of 24″ x 18″ to about 6″ across, so I had to cut out the graphs. I think it looked better, less cluttered, with the graphs gone. Empty space is nothing to fear. Sometimes it’s a problem, but I think I went overboard in trying to fill it with graphs and little annotation boxes.

“The data are interesting but I’m not convinced they need to be mapped. Is there a spatial pattern to see here, beyond the obvious one that big cities tend to have more tall buildings? Does the spatial arrangement of these cities tell us something about the data we couldn’t learn from a table? Is space causal?”

I go back and forth on this one — I think there’s possibly something spatial going on. There’s a Communist East vs. Capitalist West story throughout part of the data, though that connection is not as clear as it would be if I mapped another data set along with it, showing something economic (which would, likewise, have to have a symbol that can convey 125+ years of data). Many times a phenomenon is not driven by where on the Earth’s surface it is, but by the fact that it happens to share a location with another phenomenon. I didn’t make that as clear as I could have (I’ve got some annotation going on which helps). I think there’s also a story of spatial concentration going on here – big buildings becoming something that only big cities have, whereas many small towns had impressive structures prior to the 1950s. But, again, I don’t include a data set that really emphasizes the population differences between places.

“I would like to increase opacity behind the timelines so they don’t need to compete so much with the underlying (and irrelevant) basemap in the corners. The actual data (the lines) are easily upstaged by the basemap and fade effects.”

He’s quite right about that, in my opinion. The lines in the graphs would be easier to follow and focus on if Europe wasn’t going on behind them. Of course, I suspect that if I made the opacity higher, the graphs would start standing out too much — they’re already distracting from the main map. Another good reason to ditch them.

“I don’t know the names of any of the buildings – maybe you could label the lines (at least with some of the famous landmarks?). Without names of buildings, there is nothing to anchor my understanding to (e.g., I know the Eiffel Tower, etc.) – they’re just name-less lines around circles.”

People are probably going to be looking at this map for things that they know. Fun fact: the Eiffel Tower isn’t included here, because it didn’t fit my definition of “building” (which was a tricky thing to nail down). It’s a minor touch, but one that could give people a lot better connection to the data on this map.

One final issue that I have been thinking about lately with this project: it’s pretty complex. Look at that legend — reader education is definitely necessary before engaging with the map. It’s difficult to strike a balance between the transparency of the interface (how easily you get the data off the map) and the depth of the data. I wanted to design this as something you can stick on your wall — I wanted to give it enough substance and complexity that it’s worth examining at some length. Whether or not I have achieved that balance is something I can’t really answer, though.

Before I leave off, I wanted to point out just how much this map was affected by critique earlier down the line in the design process. Here’s what it looked like when I thought I was done:

I showed this to my boss, Tanya Buckingham, here at the UW Cartography Lab, to ask for her advice, as I was planning on entering this into some competitions. Looking back over the comments she made, I notice that she also suggested ditching the vertical timeline and combining it with the horizontal one. She also suggested getting rid of the really big coastal glow and making it more subtle, which advice I took. Drop shadows, glows, etc. should probably not scream “LOOK AT ME I DID SOMETHING FANCY!” The darker color scheme was also as a result of her urging. Both the scheme she suggested, and the one I eventually went with, do a better job of pulling the city dots out from the background and bringing the data to the front of the map.

Writing this up gives me the urge to go back and try and improve it the map, but the process is never done, I suppose. There just comes a time when you must decide it’s good enough.